Process for casting molten metal

ABSTRACT

It is herein provided to mold castings of articles, such as battery grids, in accordance with a technique for permitting the molten metal to have a higher lead content, by raising the temperature of the melt at the point of molding, or substantially thereat, but not significantly prior thereto. Accordingly, the metal is initially heated to a desired liquid conveying temperature, and, on its path of delivery to a ladle, from which it will be poured for casting, the melt is superheated, or boosted up to the desired temperature, either in a single stage, or in two stages.

United States Patent [191 Pavlo et al.

[ PROCESS FOR CASTING MOLTEN METAL [75] Inventors: William A. Pavlo,Fleetwood, Pa.;

Richard M. Conroy, Dallas, Tex.

[73] Assignee: General Battery Corporation,

Reading, Pa.

[22] Filed: Sept. 29, 1972 [21] Appl. No.: 293,461

[52] US. Cl 164/65, 164/133, 164/337,

[51] Int. Cl B22d 27/16 [58] Field of Search 164/65, 66, 68, 133, 256,164/258, 259, 335, 337, 338 H [56] References Cited UNlTED STATESPATENTS 2,060,134 11/1936 Summey 164/259 X June 11, 1974 3,467,1679/1969 Mahin 164/66 X Primary Examiner-Robert D. Baldwin AssistantExaminer lohn E. Roethel Attorney, Agent, or FirmPaul & Paul [5 7ABSTRACT It is herein provided to mold castings of articles, such asbattery grids, in accordance with a technique for permitting the moltenmetal to have a higher lead content, by raising the temperature of themelt at the point of molding, or substantially thereat, but notsignificantly prior thereto. Accordingly, the metal is initially heatedto a desired liquid conveying temperature, and, on its path of deliveryto a ladle, from which it will be poured for casting, the melt issuperheated,

or boosted up to the desired temperature, either in a single stage, orin two stages.

9 Claims, 1 Drawing Figure 24 O O O O O O O 63 PROCESS FOR CASTINGMOLTEN METAL BACKGROUND OF THE INVENTION monplace, in response to thedemands of the automobile industry, to provide batteries havingimmediate or substantially immediate high terminal voltage, forfacilitating the provision of increased cranking power, or to providethe voltage (generally 6 volts or 12 volts) at an increased amperage, inorder to effectively crank high compression engines, or engines havinglarger displacement.

In the batteries available for use by the automotive industry, namelylead acid batteries, reliance is made upon the ability of the platesurface to hold a charge, at a potential relative to other plates.Accordingly, a great number of surface charges, induced by surfacevoltage, aggregatively provide the cranking power. The greater theavailable plate surface, the more power that may be provided by abattery. One answer to this problem is to construct larger batteries, inorder to facilitate the provision of battery plates or grids havingincreased surface area. However, with the trend toward sizestandardization of components, such as batteries, for interchangeabilitywith different models of cars, irrespective of the amount of crankingpower needed or the like, as well as with the tendency towardeconomizing available space, it has become impractical, to increase thesize of batteries as an answer to this problem.

Another answer to the problem would be to increase the number of platesin each cell. To do so would require the construction of battery gridsthat are substantially thinner than those presently being utilized, inorder to permit the total surface area to be substantially increased,However, due to problems inherent in the casting of metal, and. due tolimitations in available casting equipment itself, it is impractical tosatisfactorily produce battery grids that are as thin as would berequired.

Even with conventional casting equipment, in order to keep the melt at asufficiently fluid level, having a desirably low level of surfacetension, an alloy is used in the melt, that contains not only lead, buta significant percentage of antimony. However, the presence of antimonyin the battery shortens the battery shelf life, and produces moremaintenance problems with the battery than would be the case, if thebattery were constructed of an antimony-free melt.

It is thus seen that for purposes of construction of battery grids, ithas becomecommonplace to utilize antimony in the melt, such antimonybeing provided at significant percentages, depending upon the pouring,fluid-flow situation of the melt that is desired, etc. However, it wouldbe preferable not to use significant amounts of antimony in the melt,for the abovementioned reason.

It has been found that it is possible to reduce the level of antimony inthe mel tfand to compensate therefor during the casting process, byincreasing the casting temperature, in order that the surface tension ofthe alloy will be sufficiently low to make good castings, even withalloy of low antimony content. However, at such higher temperatures,induced at the supply pot and'carried through the piping from the pot tothe ladle, such would induce excessive oxidation anddrossing, or theformation of a scum on the surface of the melt, would be the result,thereby causing casting imperfections.

THE PRESENT INVENTION The present invention is directed toward providinga system whereby low antimony content of the melt may be used, butwherein a high casting temperature is employed, but wherein such highcasting temperature is not applied until the last possible moment, priorto casting itself. This is done by first raising the temperature at thepot to a level that is sufficiently high in order to facilitateconveyance (as by pumping) throughout the delivery line, but which issufficiently low that only insignificant amounts of oxidation will occurin the melt. Then, the temperature of the melt is raised just prior tocasting, preferably in a subsequent two-stage operation, of firstraising the temperature just prior to delivery of the melt to a ladle,preferably in an oxygenfree (or substantially free) atmosphere forfurther reducing the potential toward oxidation, such boost intemperature being preferably to a level just below what would be a goodcasting temperature for the metal, followed by another boost intemperature of the metal at the ladle itself, prior to pouringthe metalfrom the ladle, into the mold.

SUMMARY OF THE INVENTION In accordance with the present invention, thetem-' perature of the melt is substantially increased after the melt hasleft the supply pot, and prior to ladling the melt into a mold, in orderto minimize opportunity for oxidation of the melt, such increasepreferably being accomplished in a superheater located just prior to theladle, for raising the temperature of the melt delivered to the ladle.

Accordingly, it is a primary object of this'invention to provide novelcasting method and apparatus.

It is a further object of this invention to provide a novel techniquefor the formation of battery grids.

. It is another object of this invention to provide a novel moldingtechnique, for molding castings having a high lead content. t v

It is another object of this invention to provide novel method andapparatus for making batterygrids having reduced antimony content,wherein a superheater is utilized for raising the temperature of themelt subsequent to the application of heat to the melt in the meltingpot.

It is a further object of this invention to accomplish the above object,wherein the step of raising the temperature occurs as part of atwo-stage operation, with the temperature first being raised in asuperheater, to

- a level just below that of the desired casting temperavart fromareading of the following brief description of the drawing FIGURE,detailed description of the preferred embodiment, and the appendedclaims.

IN THE DRAWING The FIGURE is a schematic view of an apparatus embodyingthe system of this invention, and which is adapted for performing themethod of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURE, itwill be seen that a pot is provided, for receiving lead, and a smallamount of antimony 21 therein, by a suitable chute 22 or the like, withthe material (lead and antimony) being in pellet form or the like, ifdesired, and with the pot 20 being provided with a gas burner or thelike 23, for heating metal within the pot to a desired temperature. Theburner 23 is of the open flame type, and may be provided with a fuel andair mixture for combustion or the like through a delivery line therefor24, from any suitable source, with a control valve 25 being provided inthe line 24, for a purpose which will be discussed hereinafter. 7

The temperature of the melt formed in the pot 20 will generally be about700 Fahrenheit, which is significantly lower than the temperature formelt in pots utilized in accordance with'conventional battery gridcasting techniques. In any event, the temperature of the melt in the pot20 will be brought to a sufficient level to permit fluid or liquiddelivery therefrom, by means of a suitablemolten metal pump 26 or thelike, or by any other conventional means, through a line 27, whereby themelt will be delivered to the inlet 28 at the lower end of a superheater30.

The superheater 30 is provided with a pair of gas burners 31 and 32,constructed of conventional manifold-burner arrangement, each to have aplurality of burner jets of the open flame type supplied by a suitablefuel-air or fuel-oxygen source or the like, as de- I sired, from asuitable delivery line 33, and with a control valve 34 being disposed atthe inlet of the connect-. ed-together manifolds, 31, 32. It will beapparent that, at a temperature of about 700, even a low antimonycontentlead melt in the pot 20, will not significantly oxidize.

In the superheater 30 (which is closed except for its inlet and outlet,in order to facilitate a substantially controlled oxygen atmosphere forthe heating of melt disposed therein),-the melt is raised to atemperature that may be approximately l,O00 F., but which willgenerally. be within, but about 10 F. less than the desired castingtemperature of the melt. The superheater 30 is generally cylindrical inconfiguration, and is provided with an outlet 35, at a higher level inelevation than the inlet 28, in order to facilitate the passage of thehot melt at an upper level within the superheater 30, first outwardly ofthe superheater 30, past a metering valve 36 or the like, for dischargefrom the line 37, to the ladle 38. It will be noted that the meteringvalve 36 may optionally be provided in the outlet line 35,but, ifutilized, may facilitate the provision of a metered quantity only to theladle 38, returning any excess back to the pot 20 through the line 40,thereby preventing the wasting of melt, as well as preventing theinefficient waste of energy utilized to raise such excess melt to thedesired temperature.

The ladle 38 may be of trough-like construction as illustrated, and maybe pivotable about the point 41, upon actuation of a valve 42 in fluidline 43, which would control a piston cylinder 44, for actuation of apiston therein, for tilting of the trough 38 in the direction of thearrow 45 illustrated in the drawing, when it is desired to pour the meltfrom the trough 38, However, it will be understood that any suitable orconventional means may be utilized to discharge the melt from the ladleor trough 38.

It will be noted that a manifold 46 having a plurality of open-flameburners is provided, for heating the melt within the ladle 38, just atthe point or stagein the process that the melt is adapted for pouringinto a mold 47, with the heating device 46 being supplied with afuelair, or fuel-oxygen supply from a suitable source, through a supplyline 48 therein, for controlling the amount of heat supplied to theladle 38.

It will be seen that a pyrometer, pyrotroller or the like 50, may beutilized to control the amount of heat delivered to the manifolds 31, 32of the superheater 30, by controlling the fuel-air (or oxygen) supplythereto, by control of the valve 34, from the line 51, and with themeter or control device 50 being operated in response to the temperaturesensed by a thermocouple 52 or the like disposed directly in the meltwithin the superheater 30, and connected to the device 50 by a wire 53of conventional type.

Also, the metering valve 36 may be controlled by the device 50, ifdesired, to open at the time that the temperature within the superheater30 reaches a desired predetermined level. In the alternative, themetering device 36 could be controlled manually, or by a timing deviceor the like, if desired, or eliminated altogether, and with the meteringbeing provided by the control of the pump 26, or even by the delivery ofmaterial into the pot 20, if desired.

Similarly, another pyrometer, pyrotroller or the like 55 is provided,actuated by a thermocouple 56 disposed for contact with the melt withinthe ladle 38, in order to control the temperature applied to the ladle38 by the burners on the manifold 46, by controlling the amount of fueland/or air or oxygen, delivered through the line -47, past the valve 48,by control of the valve 48.

Also, similarly a pyrotroller, pyrometer 57 or the like actuated by athermocouple 58 disposed within the pot 20, may control the valve 25,for controlling the fuel supplied for raising the temperature of themelt within the pot 20, only. to a desired level for reasons aforesaid.

It will be apparent that the various controls 50, 55 and '57 maybecontrolled in any-given sequence, or programmed by a computer or thelike 60, or other suitable control device 60.

Also, the overall control device 60 may also control the operation ofthe valve 42, by a suitable line connection 61 or the like thereto, fortiming or otherwise controlling the ejection of melt from the ladle 38,by timed actuation of the piston cylinder 44, or of any other suitabledischarge means.

It will also be apparent, that, if desired, the temperature of the meltwithin the superheater 30 may be raised in a single stage (eliminatinguse of the manifold and burner arrangement 46), such that once the meltwas delivered to the ladle 38, it could be ladled there'- from, into thecasting mold 47, without further increase in temperature. In that event,the temperature of the melt would be raised by the superheater 30, to atleast (or above) the desired pouring temperature. However, in thepreferred arrangement, and in the preferred utilization of thisinvention, the temperature increase will take effect in two stages, thefirst being in the superheater, to within about 10 of pouringtemperature, with the latter 10 increase occurring while the melt iswithin the ladle 38, immediately prior to pouring therefrom.

The apparatus and process of this invention makes a significant steptoward eliminating the burning of antimony in the lead pot that alsocauses drossing, by the use of a lead pot 20 that is kept at atemperature significantly below that of prior art types.

A further advantage of this invention, is in a saving that is effectedin the alloy, in that, by the significant reduction of drossing, asubstantial weight of the alloy is usable, and does not form a scumwhich would have to be removed unless contamination were tolerable. Asignificant factor in this elimination or reduction of drossing is thatthe alloy is raised a significant amount, and at a significant level(about 300 to 400) in a controlled oxygen atmosphere (which meansoxygen-free or substantially oxygen-free) within the superheater 30, inthat the superheater 30 is closed to air (and oxygen) intermediate itsends except for the inlet 28 and discharge 35 thereof and any oxygeninitially present therein will be driven off during an early heatingstage thereof.

The mold 47, after discharge of the melt thereinto, may then bedelivered along a conveyor 63 or the like, to cooling. i

While various modifications may be made in the details of construction,as well as in the use and manufacture of the system and devicestherefor, in accordance with this invention, it will be clear that thisinvention, both in process and in apparatus form, is of a broad nature,having application to the molding of lead alloy articles, aswell as tothe manufacture of battery grids, and also to metallic castinggenerally. For example, electric heating or other types of heating inlieu of any of the heating means 23, 31, 32 or 46 may be utilized, anddumping from the ladle 38 could also be controlled by the pyrometer 55actuating the valve 42, instead of the device 60 performing suchactuation. Thus the thermocouple 56 would sense when the ladle 38 shouldbe pivoted, and initiate such pivoting. Accordingly, variousmodifications are all within the spirit and scope of the invention asrecited in the appended claims.

What is claimed is:

1. A method of molding castings comprising the steps of initiallyproviding a metallic casting material, then heating the casting materialto a first temperature sufficient to allow liquid delivery thereof, lessthan the desired molding temperature, and below oxidation temperaturesof said casting material, conveying the mo]- ten casting material to aheatable receptacle means and superheating the casting material to asecond temperature above the first temperature and at least equivalentto the desired casting temperature of the material just prior to ladlingof the material to a mold, and ladling the material at at least thedesired casting temperature into a mold.

2. The method of claim 1 wherein the method is specifically adapted formolding battery grid castings and the like, wherein at least a portionof the superheating step takes place in a controlled oxygen atmospherefor minimizing the formation of oxides on the surface of the moltenmetallic material.

3. The method of claim 1, wherein the superheating step takes place in atubular device disposed in line between the location of initiallyheating the material and the ladling thereof, and wherein saidsuperheating step comprises application of open flame to the tubular de-Vice.

4. The method of claim 1, wherein the superheating step comprises afirst stage of heating the material just prior to delivery thereof tothe ladle, to a temperature close to, but below a desired castingtemperature of the material and a second stage of heating the materialin a ladle, to at least the desired casting temperature of the material.

5. The method of claim 4, wherein the heating in the first stagecomprises bringing the material to a temperature aboutl0 less than thedesired casting temperature, at a location just prior to the location ofheating in the ladle.

6. The method of claim 5, wherein the method is specifically adapted formolding battery grid castings and the like, wherein at least a portionof the superheating step takes place in a controlled oxygen atmospherefor minimizing the formation of oxides on the surface of the moltenmetallic material, wherein the superheating step takes place in atubular device disposed in line between the location of initiallyheating the material and the ladling thereof, and wherein saidsuperheating step comprises application of open flame to the tubulardevice.

7. The method of molding battery grids and the like of molten metal thatincludes at least lead material comprising the steps of first heatingthe material to a desired pumping temperature, just sufficient to allowpumping thereof, pumping the heated material to a superheater thensuperheating the material in a superheater of controlled oxygenatmosphere, to a temperature close to the desired casting temperature,delivering the superheated melt to a ladle, again heating the materialin the ladle to at least a molding temperature, and pouring the materialfrom the ladle into a mold.

8. The method of claim 7, including the steps of separately controllingthe amount of heat applied to the material at the superheater and at theladle.

9. The method of claim 1, wherein the superheating step includessuperheating an amount greater than that needed for a given casting andreturning the excess to the location of initial heating.

1. A method of molding castings comprising the steps of initially providing a metallic casting material, then heating the casting material to a first temperature sufficient to allow liquid delivery thereof, less than the desired molding temperature, and below oxidation temperatures of said casting material, conveying the molten casting material to a heatable receptacle means and superheating the casting material to a second temperature above the first temperature and at least equivalent to the desired casting temperature of the material just prior to ladling of the material to a mold, and ladling the material at at least the desired casting temperature into a mold.
 2. The method of claim 1 wherein the method is specifically adapted for molding battery grid castings and the like, wherein at least a portion of the superheating step takes place in a controlled oxygen atmosphere for minimizing the formation of oxides on the surface of the molten metallic material.
 3. The method of claim 1, wherein the superheating step takes place in a tubular device disposed in line between the location of initially heating the material and the ladling thereof, and wherein said superheating step comprises application of open flame to the tubular device.
 4. The method of claim 1, wherein the superheating step comprises a first stage of heating the material just prior to delivery thereof to the ladle, to a temperature close to, but below a desired casting temperature of the material and a second stage of heating the material in a ladle, to at least the desired casting temperature of the material.
 5. The method of claim 4, wherein the heating in the first stage comprises bringing the material to a temperature about 10* less than the desired casting temperature, at a location just prior to the location of heating in the ladle.
 6. The method of claim 5, wherein the method is specifically adapted for molding battery grid castings and the like, wherein at least a portion of the superheating step takes place in a controlled oxygen atmosphere for minimizing the formation of oxides on the surface of the molten metallic material, wherein the superheating step takes place in a tubular device disposed in line between the location of initially heating the material and the ladling thereof, and wherein said superheating step comprises application of open flame to the tubular device.
 7. The method of molding battery grids and the like of molten metal that includes at least lead material comprising the steps of first heating the material to a desired pumping temperature, just sufficient to allow pumping thereof, pumping the heated material to a superheater then superheating the material in a superheater of controlled oxygen atmosphere, to a temperature close to the desired casting temperature, delivering the superheated melt to a ladle, again heating the material in the ladle to at least a molding temperature, and pouring the material from the ladle into a mold.
 8. The method of claim 7, including the steps of separately controlling the amount of heat applied to the material at the superheater and at the ladle.
 9. The method of claim 1, wherein the superheating step includes superheating an amount greater than that needed for a given casting and returning the excess to the location of initial heating. > 